Mine roof stress indicating bolt



July 5, 1960v v. A. CURRY 2,943,528

MINE ROOF STRESS INDICATING BOLT Filed Oct. 29, 1957 A INVENTOR.

.I" VIRGIL A. CURRY +5 Jg' 7 ATTORNEY.

United States Patent MINE ROOF'STRESS INDICATING BOLT Virgil A. Curry, Dehue, W. Va.

Filed Oct. '29, 1957, Ser. No. 693,0.621: 3 Claims. (Cl. 85-62) This invention relates especially to mine-,roof plate:

supporting-bolts and the like and is particularly directed to securing-tmeans' for mine roof plates, for example thosetof -the character disclosed in the copending appliwrenchrland integralimeanszafiording a visual indication cation for United States Letters Patent Serial No. 591,

397, now ,Patent No. 2,854,824, filed June 14, 1956, allowed Februaryll, 1958, of William C; Campbell and the herein named-Virgil A. Curry entitled Mine Roof.

Bolt Plate.

As described in said application, wherezmine roofs require support to supplement inherent stability usually rigid plates are secured tothe roof by upwardly extending bolts sometimes up to 5' or6' or more in length anchored/tosuperjacent earth or rock strata with their. entire length, ,except for a protruding head substantial-' ly enclosed-within thebores provided for their reception.

comprising a abolti head :adapted for reception of a of attainmentiof'the proper degree of-internal tension on the llfllt dlll'il'lgi the operation of. securing, for example, aroof plate to. aimine roof'throughthe instrumentality thereof: 1'

A further. objectis'r-tozprovideen al=mine roof bolt head 3 an integralszfiangeflor flashv the characteristics of which can be fixed during manufacture to indicate-by its deformation duringrusetting up of the bolt whenthe proper tensionon: the latter has been :attained; 4.

Other objects; purposesand advantages 10f :the invention will hereinafter moreifullyzzappear zonxberunderstood from the following-descriptionzbf L certain'i embodiments thereofwas illustrated 'rin' the accompanying .drawi'ngfin which:

Fig. -1:. .is airfragmentary;diagfammaticnsectiontof a mine roof showingone of; my novelx'bolts securing a typical,roof,--plate thereto; a

Fig. 2j is an enlarged fragnientaryxside elevation 10f one of the bolts before installation;

Fig. 3 is a similar view in.a.;planei9 0; frointhe.plane of Fig. 2;

Fig. 4 is an-end elevations-ofithe bolt head" ofF-igs. 2 and 3;:and

Figs.-5,=6 and 7 are viewsrcorresponding to Figs.2, 3

and 4 but showinga modified:,.construction of the bolt head flashp A suitable expansion shield or shell is normally threaded on the bolt shank and expanded against the borejwall by rotation of-;the bolt, and with mechanical wrenches generallyv employed for turning the bolts it'is oftendifficult to determine whether the bolt has been properly set up in the shell to secure the plate permanently to the mineroof -It has therefore *been necessary for'installers merelyto estimate on the basisof little more guidance than that obtained-fromexperiencewhether too much, too little;or. -.just the correct-amount of torque has been applied itOnllhe bolt headlto afliord maximumsecurity.

Referring now moreparticularly-to the drawing, Pig. 1' illustrates -abolt 1 installed in amine roof R "and securing. atypical roof "plate'P.-thereto-but after the tension indicating-componentsof the bolt-have beeri' distorted during installation,- and :as it depicts as' nearly as practical the appearaneemflone such'eornponentwhether initiallylcomprisedin the boltrepresentedin- Figs. 2-4 or that ofilFigs. 5"7, a description ofmthe s'aidbolts before being installed will herein precede a more detailed explanation.with-refereneeitoi Fig.--1; of.-the effectswof in- Special -wrenches. designed-to apply a predetermined torque sare not always accurate-and cannotbe relied feet a pair of axially aligned heads with ashear zone, between them designed to 'rupture on application of pre- 1 determinedtorque are thus unsatisfactory, since no: al-

lowancecan be. made for variable factors, principally friction, which prevent torque being directly and uniformly related to .tension stress.

As it is obvious that too much torque and/or the tension vector resulting therefrom may weaken the bolt and foreshadow its failure or:.cause rupture of the rock surrounding 'the shell .while too little may be insufiicient to lock the. shell securely in the bore or to draw the roof plate tightly againststhe roof, it is apparent that unless the correct amount of tension stress is appliedto the bolt the heavy roof platernay at an unforeseeable moment fall from the roof at the risk of injury to operatives engaged below and otherwise, particularly when'the plate is used to""support;utility lines, cause serious disruption of miningnperations or even collapse of a part of the provide a novel bolt for a mine roof plate or the like stallation rupon' theme ThusinFigsf 4 M; whichmaybe of any i able length having a shank-wz provided withwthreadslnot shown) =is.:formed integrally' with ahead -3--and an'inter- I mediate circular or. annular .flangever'wflashd projecting radiallyoutward slightlyf beyond the outer corners of the head-proper,--which1 is of course-usually:polygonal I (square in the drawinglto allowsa wrench=to be readily=-' The flange and bolt head may lbe readilwformed by known applied for turning: the bolt during installation,

proceduresasl-by upsettingswhile hot the end portion of. the rod stock-of-which the bolt is made. If desired the upsetting zdies m-ayrproduce simultaneously with the fash-" 1 ioningtof the flange aplurality;.preferably:a-diarnetricah" ly opposedpair, of indentations 5 .which are concavelyarcuateinnform inthe bolt shown:in-Figs.- 2-4 at the U edges of-the flange but merge with the head' and flange approximately-.inthe plane-of the adjacentsides-of the bolt headproper forming on the opposite'sideof the flange generallycomplementary convexprojections 6; a

It will of course of apparent the flange may bernade flat initiallyand subsequentlydeformed top-reduce the indentations and projectionsdfdesired and that the axial thickness. of the flange may be a matter-.of, choice. de pending on a number of factors hereinafter more .fully.

explained.

The bolt illustrated in.Figs.P5-7 is: closely similar to that just described, comprising a'shank" 2', head 3 and flange or flash '4, the latter, ihoweveryinstead of havingarcuately shaped indentations and projections "has compara tively flat sided indentations "5 forming'projections 6' the side faces of'which makeam-angleconverging in the direction of the threadedend of'the bolt, small trihedral 3 figures 7 in Figs. 5 and 7 indicating generally the complement of a working portion of a forming tool used in their production.

These bolts, both styles of which may be used interchangeably although that shown in Figs. 2-4 will perhaps be preferred in most situations, are designed to have the indentations and projections in their flanges flattened out substantially to alignment with the remainder of the flange when installed in a mine roof or the like, resulting in merely slight irregularities indicated at 8 in Fig. 1 which have substantially the same appearance no matter which specific bolt is used initially, and it would therefore be impractical to attempt in Fig. 1 to illustrate any difierences. In each case, however, the flange is proportioned and its indentations and projections designed to flatten out as described when subjected to substantially the optimum tension it is desired to place on the bolt on installation.

This matter of tension is of extreme importance in mine roof plate bolts, and as indicated it has heretofore been impossible to obtain any reasonable degree of accuracy in controlling or determining it on the basis of torque applied. However the indicating means of my invention are preferably initially designed with reference to the inherent characteristics of the metal contained therein and the tension deemed most suitable to be applied to the bolt on installation.

It will of course be understood that in an installation of either bolt in a mine roof its shank is passed through a roof plate P and a suitable expansion nut or shell S threaded on its extremity. If desired a flat annular washer (not shown but of any convenient size) may be interposed between the bolt head and the plate before the shell is threaded on the shank. The latter, with the shell and plate, is then inserted in a previously prepared bore B in the mine roof wherein the outer components of the shell initially engage the rock or other formation in which the bore is formed with adequate friction to cause their separation when the usually wedge shaped inner component of the shell, threaded on the shank, is drawn to+ ward the bolt head through turning of the bolt by a wrench applied thereto.

It will be apparent that as the bolt is tightened to draw the head, and hence the roof plate, toward shell S after the latter by its expansion has become fixed in bore B, the projections 6, 6 as the case may be bear against the roof plate, or against a washer bearing on the latter if one is used, and as the tension on the bolt increases the projections and their corresponding indentations therefore tend to flatten out, the point at which this occurs being determined by initial characteristics such as the material of which the flange is made, its thickness, the configuration of the indentations and projections, and other inherent factors, as well as the pitch of the bolt threads, the torque available, friction between the projections and the plate or washer as the case may be, as well as the capacity of the shell to resist opposite axial movement by its frictonal engagement with the adjacent roof stratum. It is usually advisable to provide a lubricant to minimize friction between the projections and the surface on which they bear as excessive friction at these points substantially enhances the torque required for turning the bolt yet without transmission of corresponding torque to the bolt shank.

As has been explained, the projections on the bolt flange are so designed as to substantially return to the plane of the flange when the bolt has been set up sufliciently to subject it to the desired tension and thus afford to the man installing the bolt a readily visible indication of the attainment of that condition. Thus by merely observing the projections and corresponding indentations after the former engage the roof plate, or washer if one be used, the installer is apprised when to discontinue application of further turning force to the bolt to avoid overstraining of the latter or possible over-expansion of the shell with 4 consequent exertion of undue stress agianst the bore hole wall, crumbling of the surrounding strata and even release of the shell.

The numerous factors which may be affected adversely by improper installation of mine roof plates and the dangers to which mining operatives may be exposed on failure of even one bolt, either from too much or too little tension being applied at its installation suggest the invention may find its primary utility in this field, but it is not intended that its usefulness be restricted thereto as it may find application in many other situations Where secure fastening means are required and may be particularly related to the axial vector of torque applied to a threaded element. For example, where a nut is accessible it may be preferred to incorporate therein the flange with its projections and indentations, here described with relation to a bolt head; illustration of such a nut, however, would involve only duplication as to all essential features and is therefore superfluous.

While I have used torque herein as in some instances perhaps directly indicating, or comprising a function of the tension stress on the bolt when the projections and indentations have become substantially flat, it will be understood there is not necessarily a fixed or mathematically determinable relation between them since a number of factors may interfere with the direct resolution of applied torque to tension stress, including friction between the projections and plate, or in the threads of the bolt and shell, torsional resiliency of the bolt itself, particularly when an unusually long one is used, as well as possible frictional yielding of the shell in engagement with the 'wall of the bore. As deformation of the projections and indentations provided by my invention is a direct function of the tension stress on the bolt, however, friction in this relationship being but an insignificant and substantially constant factor, particularly if a suitable lubricant be used, it is apparent that their flattening as a. result of applied torque affords a direct and readily observable indication that the tension stress at which they were designed to yield has been attained.

It is therefore advisable that the indentations and projections be carefully controlled during manufacture, not only with regard to the physical properties of the material of which the flange in which they are formed is made, but also as to the thickness of the flange and the depth, configuration, radial length and other characteristics of the indentations themselves. Thus the designer should be fully apprised of the physical properties of the material used as well as the service conditions expected to be encountered, particularly the tension stress on the bolt at which the indentations are to be designed to yield and'it is then but a matter of routine calculation to determine the dimensions of the flange, projections and indentations required to meet the assumed conditions.

While I have herein described certain embodiments of the invention with brief reference to other possible variations in design and practice, it will be understood I do not thereby desire or intend to limit or confine myself thereto or thereby in any way as other changes and modifications in the form, construction, operation and relationship of the parts of the threaded securing means embodying my invention which, as above indicated, I consider appropriate for embodiment in nuts as well as in blots, will'readily occur to those skilled in the art and may be availed of as desired without departing from the spirit and scope of the invention as defined in the appended claims.

Having thus described my invention, I claim and desire to protect by Letters Patent of the United States:

1. A mine roof stress indicating bolt comprising a shank threaded adjacent one end for cooperation with an internally threaded nut seating in a bore in a mine roof, a head at the other end of the shank and integral therewith for reception of a Wrench for turning the bolt, said head having a flat face proximate the shank, and a flash integral with the head projecting normal to the shank beyond the periphery of the head having a fiat roof plate engaging face coplanar with the fiat face of the head except for portions in diametrically opposed areas indented in its face remote from the shank to provide in its roof plate engaging face generally radially directed projections extending from its edge and terminating short of the shank adapted to engage a mine roof plate when disposed about the shank between the flash and said nut and as the bolt is turned into the latter when drawing the plate against the mine roofto ultimately permanently recede into and remain in the plane of the flash to thereby afford visible indication that a predeterrm'ned tension has been imposed on the bolt.

2. A mine roof stress indicating bolt of uniform composition comprising a shank threaded adjacent one end for cooperation with an internally threaded expansion nut seating in a bore in a mine roof, a head at the other end of the shank and integral therewith for reception of a wrench for turning the bolt, said head having a flat face proximate the shank, and a flash integral with the head projecting normal to the shank beyond the periphery of the head having a flat face in part coplanar with that of the shank but deformed in diametrically opposed areas in its face remote from the head to provide generally radially directed projections extending from its edge and terminating short of the shank in that face of the flash coplanar with said flat face of the head, said projections conforming in transverse section to closed convex arcs, being united to the adjacent body of the flash throughout their respective perimeters and adapted to engage a mine roof bolt plate when disposed about the shank between the flash and said nut and as the bolt is turned into the latter when drawing the plate against the mine roof to ultimately permanently recede into and remain in the plane of the flash when a predetermined tension has been imposed on the bolt and thereby provide a visible indication of the attainment of that condition.

3. Mine roof bolt tension indicating means comprising a bolt having a threaded shank entering a nut anchored in a mine roof, a roof plate interposed about the shank between the head and the roof, 2. head integral with the bolt shank disposed below said plate, said head having a flat face for engaging the roof plate, a flash integral with and projecting radially beyond the periphery of the head, said flash having a roof plate engaging face coplanar with the flat face of said head except for portions indented in its face remote from the shnak to provide diametrically opposed radially directed uninterrupted projections in its roof plate engaging face adapted to engage the plate when the bolt is turned sufliciently into the nut and on further rotation of the bolt to gradually flatten out into the general plane of the flash to substantial permanent coincidence therewith when the bolt is stressed to a predetermined degree thereby affording a visible readily observable indication of the attainment of such stress condition.

References Cited in the file of this patent UNITED STATES PATENTS 1,875,930 Martin Sept. 6, 1932 1,952,600 McComb Mar. 27, 1934 1,956,745 Payne May 1, 1934 2,632,355 Becker Mar. 24, 1953 2,781,687 Knocke Feb. 19, 1957 FOREIGN PATENTS 447,143 France Oct. 19, 1912 108,937 Great Britain Aug. 30, 1917 

